> The UBS GNT has the advantage of having the companion volume
> "A Textual Commentary on the Greek New Testament" by Bruce
> Metzger, which explains, verse by verse, why the committee
> valuated the text the way they did -- something one can't get
> for the NA27.

Sorry for my muddy speech. Because the Greek texts of the NA and the UBS
are the same, Metzger's commentary on the Societies' preferred reading
applies to BOTH (but only to those variants shown in the UBS and not
those in the NA). Hence, it does not present an advantage unique to the
UBS.

The Am. Bib. Soc. now again has the NA27 available. The NA27, the UBS4,
and Metzger's textual commentary are each $22.99.